Field of the Invention
The present invention relates to a control device for a hybrid vehicle which controls a hybrid vehicle comprising both an internal combustion engine and a motor as driving sources of the vehicle.
Description of the Related Art
A hybrid vehicle (which may be simply referred to as a “vehicle” hereafter) comprising both an internal combustion engine (which may be simply referred to as an “engine” hereafter) and a motor as driving sources of the vehicle is known. The vehicle comprises a storage battery, and the storage battery supplies electric power to the motor, while it is charged with output power of the engine.
In addition, when rotation of an axle is transmitted to the motor, a generator generates electric power (namely, the motor generates electricity), and the storage battery is charged also by the electric power. That is, kinetic energy of the vehicle is converted into electrical energy, and the electrical energy is collected by the storage battery. This conversion of energy may be referred to as “regeneration.” When the regeneration is performed, braking force of the vehicle which the motor generates (namely, torque which decelerates vehicle speed) may be referred to as “regenerative braking force”, and braking of the vehicle using the regenerative braking force may be referred to as “regenerative braking.” Electric power collected in the storage battery by the regenerative braking may be referred to as “regenerative electric power.” When energy is collected in the storage battery by performing the regenerative braking at the time of deceleration of the vehicle, fuel consumption (specific fuel consumption) of the vehicle can be improved.
On the other hand, a remaining capacity SOC (State of Charge; which will be simply referred to as an “SOC” hereafter) of the storage battery changes during a running of the vehicle. When increase and decrease of the remaining capacity SOC are repeated when the remaining capacity SOC is in either one of a state where the remaining capacity SOC is high and a state where the remaining capacity SOC is low, deterioration of the storage battery is promoted. Therefore, during a running of the vehicle, a control device for a vehicle sets a target remaining capacity to a suitable value between a remaining capacity upper limit and a remaining capacity lower limit, and controls the engine and the motor so that the remaining capacity SOC approaches the target remaining capacity.
By the way, when a vehicle runs a downward slope, generally, a driver takes a foot off an accelerator pedal and further steps on a brake pedal in some cases (according to circumstances). At this time, a control device for the vehicle suppresses increase of vehicle speed using regenerative braking force and, thereby, raises a remaining capacity SOC.
When the remaining capacity SOC increases (i.e., when an electric power amount charged in a storage battery increases), a distance for which the vehicle can run only with output power of a motor with an operation of an engine stopped becomes longer. Therefore, if the remaining capacity SOC can be increased as much as possible in a range which is less than a remaining capacity upper limit when the vehicle runs a downward slope, fuel consumption of the vehicle can be raised further.
However, since the remaining capacity SOC reaches a remaining capacity upper limit soon when a downward slope is long, it becomes impossible to increase the remaining capacity SOC increase further. Therefore, the larger difference between the remaining capacity SOC and the remaining capacity upper limit at a starting point of the downward slope is, the larger fuel consumption improvement effect obtained by running a downward slope becomes.
Then, when a downward slope segment which has a predetermined difference of elevation exists on a scheduled traveling route, one of conventional control devices for a hybrid vehicle (which may be referred to as a “conventional device” hereafter) gives priority to a running in which an operation of an engine is stopped and only a motor is operated over a running in which both an engine and a motor are operated so that a remaining capacity SOC approaches a remaining capacity lower limit as much as possible before a vehicle goes into the downward slope segment (refer to the Patent Document 1 (PTL1)). Hereinafter, a running in which an operation of an engine is stopped and only a motor is operated may be referred to as an “EV running”, and a running in which both an engine and a motor are operated may be referred to as an “HV running.”
In accordance with this conventional device, since the remaining capacity SOC is made lower than that at normal time during a period when the vehicle is running a segment before the vehicle arrives at a starting point of the downward slope segment (which may be referred to as a “pre-use segment” hereafter), use frequency of the engine during the period falls. Furthermore, since the difference between the remaining capacity SOC and the remaining capacity upper limit becomes larger at the starting point of the downward slope segment, more electric power can be collected during the running of the downward slope segment. Therefore, the use frequency of the engine thereafter also falls. As a result, the fuel consumption of the hybrid vehicle can be improved.
On the other hand, a technology referred to as an “extended regeneration control” is also known in the art. When it is predicted that a vehicle slows down based on the information about a driver's operation tendency (for example, deceleration action, etc.) and a location of a vehicle, etc., a control device which performs the extended regeneration control sets a point where it is predicted that the deceleration of the value will be ended as a target deceleration ending point. Furthermore, the present control device increases a regenerated electric power amount by setting a suitable deceleration starting point and increasing regenerative braking force from the deceleration starting point, so that the regenerated electric power amount becomes larger during a deceleration running to this target deceleration ending point (in other words, so that an amount of consumption of energy by braking using a friction braking device resulting from performing a rapid deceleration becomes smaller) (refer to the Patent Document 2 (PTL2)).
Thus, since the extended regeneration control can raise the remaining capacity SOC further, a distance for which the EV running is possible becomes longer. Therefore, the fuel consumption of a hybrid vehicle can be further improved by adopting the extended regeneration control.